Radioactive source



lrwentfo: warnerwchulbz, Eu ene P Kozoriz,

His Attorney.

RADIOACTIVE SOURCE Filed Dec. 6, 1950 W. W. SCHULTZ ET AL Nov. 13, 1951v Patented Nov. 13, 1951 y1de;applications"forradioactive sourceseXistin'bthvmedicineand industry-,filmt heretofore 'e tfis lfan''obj'ect'fof-f this f-invention; therefore;Y to rovd-n'ewland improved means.'vfor housing a -I'irsoure'e oradioactivity.

Anptheiob'ject ofthis inventionis tdprovide a structionzand i'ow inexpense.

Afurtnereobject" ofi this inventionfisto :provide aaradi'o'a'ctivesourceih'avin'g aiphysicalib'alirie of uc'i'ent Jstrength'15o-safelycontain the radioacagentA usefuluradiation. @In 'accordance' withi thisinvention, afdeposit of A.. radioactive "material placed on aflat'surface offer-'supporting block -formed -of a `substancei lsuch asmetalfor resinous materialfeig., fiberglass f. -r llaminate,v which is:not readily broken down: by

.fprolongedbombardment from radioactive matet P-rials. "f1-he natsurface and the radioactive-layer v a are -coveredby-r a `thinfsheet ofsealing -material,

lwsnhasv-.micaftransparent to the spectrum of'- adiationfromthehradioativematerial, the sheet iff di s eal-ingfmateri-ai beingbonded t0 the-fiat surface by a thin layer oran-adhesive agent such asaspolyepoxide Vresin` or-a low melting glass composition. Thersupporting-block With its-radio v@active sur-face andA thin coveringsheet is placed a ma casing-made `of some material, such asfor "example,stainless steel, capable offwithstanding H prolonged bombardment fromnuclear particles land is bonded therein by a layer of adhesive. The

v --fcasm`g has-anaperture or Window over theerado- 'fctiveportion ofthe surfacetopermitthe radiaionsto escapei For furtherfsafety,thisrst'casmgimaybe placed Within a'similarsecond casing. the fsecondroroutercasing #hasr a1 windowieon.

inentof `the leaks', they absorbthe softe'rilradiaive'inateralyetthinfenough to. permit thelp'as- @in housing-f forting: block v2"contains" an material is deposited in solution within the con`"bardment from radioactive materials; more speciiically, these otherresins frequently become friable or turn into powder. The qualities ofthe polyepoxide resins which make them particularly desirable in thisapplication are that they have no volatile by-products on condensationor polymerization; they have no initial solvents; they setiat roomtemperatures and have a reasonably fast room cure, for example, 4 hoursat 70 F. Other preferred adhesive or bonding agents are low meltingglass compositions. To be satisfacnes of moat 3. Then, the solution isevaporated,

leaving radioactive layer 5.' During the 'evapo-4 ration process,chimney I3 can be fitted intomoatf 3 to prevent the spread ofradioactivity tolother parts of supporting block 2. Other methodsofdepositing radioactive layer 5 may, of course, be used. Electroplatingwould be one such method. However, for electroplating to be used, block2 must be constructed oi?r a conducting material. If electroplating isemployed to deposit radioactive layer 5, moat 3 can be eliminated fromsurface 4, since there is then no evaporation process to oifer.contamination to surrounding areas.-

To continue with the method ofconstructing housing I, once radioactivelayer 5 is deposited on the portion of surface 4 enclosed by moat 3, avery thin sheet 6 of material is placed over and bonded to surface 4.Sheet 6 must be of such a type that it forms a sealing layer transparentto the useful spectrum of radiation from radioactive layer 5. In thepreferred embodiment of this invention, sheet 6 is a sheet .of mica butother materials may be employed.V

y Thepurpose of sheet 6, as placed over surface 4, is to serve as abarrier to hold radioactive layer 5 thereon, since the'escape of anypart of layer 5 would present -a serious health hazard. The sheet ofmaterial-must be keptextremely thin where alpha, beta orbeta-gammafemitters are employed, in order that the alpha or beta.particels will not be absorbed. For low energy gamma or X-ray emitters,the same requirement also exists. `Since mica can be split intoextremely thin sheets, sometimes even only a few molecules thick, it isan excellent material for coated with adhesive layer 6a. Sheet 6 is thenpressed on surface 4, moat 3 actingV as a trap vfor any radioactivematerial that is squeezed sideways, thus further preventingcontamination of any other parts of block 2. The bonding agent not onlyholds sheet 6 in place, but also by mixing with radioactive layer 5tends to prevent any movement therein. This is important in that ifsheet 6 should be punctured, only the small'bit of radioactive materialdirectly underneath 'the puncture may escape, nor matter in whatposition housing I is placed.

This method of depositing radioactive layer 5 within the connes of moat3 and then bonding it in place with adhesive layer 6a under sheet 6prevents, as far as possible, the escape of radioactive material in boththe construction and use of Housing I. A presently preferred adhesive orbonding agent is a resin of the polyep'oxide class. By a polyepoxideresin it is meant any one of the class of thermosetting resins capableof form ing large macromolecules, i. e., resins whichare capable ofbecoming highly cross-linked upon polymerization. It is'preferable touse'a highly cross-linked resin because most other'resinsvlose theirphysical properties more readily under bomtory, a glass composition mustbe capable, when liquid; v'of wetting both surface 4 and sheet 6.y It

- should also have a'coefhcient of expansion, when solidiiied, intherorder of those of surface 4 and sheet 6 so that appreciable physicalstresses will sion-resistant, such as stainless steel, is about theAbest material which can be used for casings l and 9. ,Howeven althoughcasings l and Bare preferably metallic their compositionis notnecessarily restricted to metal. There fare a number of non-metallicsubstances which can stand prolonged bombardment from radioactivematerials, and casings which will give satisfactory results can= beformed from those non-metallicl sub- Y stances. For example,casings'formed of plastics can be substituted for Ythe metallic casings,il' desired. i

Casings 9 and II and block 2 together cut oiI almost all radiationsexcept those in the desired direction, and, due to the double casingconstructionyit is almost impossible for radiation leaks to develop,unless housing I is severely damaged bysome meanasuch as rough handling.

S- For some applications, only one casing may ybe necessary, while instill other' applications more than two casings may be desirable. t Thisiny vention is not to be construed as restricted -to a structure havingtwo casings; one casing or a plurality of casings contained one withinYan-YAY other may be employed as necessary, theinnermost casing, ofcourse, containing the supporting block, the sheet of sealing materialand the radioactive deposit contained therebetween.

, While there has been described what, at present, is considered to bethe preferred embodiand modications as fall within the true spirit fromsaid deposit ofradioactive material; `ailayerk ,y

of adhesive bonding said sheet of sealing material to said surface; acasing formed of material capable of standing prolonged bombardment fromradioactive material containing' said snpporting block, said sheet ofsealing material and said deposit of radioactive material bondedtherebetween and having an aperture positioned over said deposit ofradioactive material; and a layer of adhesive bonding said supportingblock and said sheet of sealing material to said casing.

2. A radioactive source comprising a supporting block formed of amaterial not readily broken down by prolonged bombardment fromradioactive materials and provided with a at surface containing anendless moat;a deposit of radioactive material on the portion of saidflat surface surrounded by said moat; a sheet of sealing materialcoveringsaid surface and said deposit of radioactive material thereon toform a sealing layer transpartent to the spectrum of radiation from saiddeposit of radioactive material; a layer of adhesive bonding said sheetof sealing material to said surface; a plurality of casings formed ofmaterial capable of standing prolonged bombardment from radioactivematerials and contained one within another, the innermost of saidcasings containing said supporting block, said sheet of sealing materialand said deposit of radioactive material contained therebetween, saidcasings having concentric apertures positioned over said deposit ofradioactive material; layers of adhesive bonding said casings to eachother, and a layer of adhesive bonding said block and said sheet ofmaterial to said innermost casing.

3. A radioactive source comprising a block of resin-bonded fiberglasslaminate provided with a flat surface containing an endless moat; adeposit of radioactive material on the portion of said flat surfacesurrounded by said moat; a sheet of mica covering said surface and saiddeposit of radioactive material thereon; a layer of a polyepoxide resinbonding said sheet of mica to said surface; an inner casing and outercasing both formed of material capable of standing prolonged bombardmentfrom radioactive materials, said outer casing containing said innercasing and said inner casing containing said block, said sheet of micaand said deposit of radioactive material contained therebetween, saidcasings having concentric apertures positioned'over said radioactivedeposit; a layer of a polyepoxide resin bonding said block and saidsheet of mica to said inner casing; and a layer of a polyepoxide resinbonding said inner casing to said outer casing.

WARNER W. SCHULTZ. EUGENE P. KOZORIZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,405,026 Feuer et al July 30,1946 2,476,644 Wallhausen et al. July 19, 1949 2,479,882 Wallhausen etal. Aug. 23, 1949 FOREIGN PATENTS Number Country Date 467,924 GreatBritain June 25, 1937

1. A RADIOACTIVE SOURCE COMPRISING A SUPPORTING BLOCK FORMED OF AMATERIAL NOT READILY BROKEN DOWN BY PROLONGED BOMBARDMENT FROMRADIOACTIVE MATERIALS AND PROVIDED WITH A FLAT SURFACE; A DEPOSIT OF ARADIOACTIVE MATERIAL ON A PORTION OF SAID FLAT SURFACE; A THIN SHEET OFSEALING MATERIAL COVERING SAID SURFACE AND SAID DEPOSIT OF RADIOACTIVEMATERIAL THEREON TO FORM A SEALING LAYER TRANSPARENT TO THE SEPECTRUM OFRADIATION FROM SAID DEPOSIT OF RADIOACTIVE MATERIAL; A LAYER OF ADHESIVEBONDING SAID SHEET OF SEALING MATERIAL TO SAID SURFACE; A CASING FORMEDOF MATERIAL CAPABLE OF STANDING PROLONGED BOMBARDMENT FROM RADIOACTIVEMATERIAL CONTAINING SAID SUPPORTING BLOCK, SAID SHEET OF SEALINGMATERIAL AND SAID DEPOSIT OF RADIOACTIVE MATERIAL BONDED THEREBETWEENAND HAVING AN APERTURE POSITIONED OVER SAID DEPOSIT OF RADIOACTIVEMATERIAL; AND A LAYER OF ADHESIVE BONDING SAID SUPPORTING BLOCK AND SAIDSHEET SEALING MATERIAL TO SAID CASING.